HI.....I need an amplifier circuit for my electret microphone so that it is very sensitive to different voices.With microphone as analog input I should get wide range of numbers on serial monitor sensitive to different voices.

You could however filter the signal, say with six band-pass filters and 'recognise' different voices from their spectral components. Even better might be to use the arduino fft library. I doubt it will actually provide per-person recognition, but with some tweaking you might be able to distinguish a male voice from a female's, or a child's voice from an adult's.